Field of the Invention
The present invention relates to inspection/adjustment of a laser beam output optical unit and inspection of a laser scanning optical system, which are used in, e.g., a laser beam printer (LBP) which performs recording by scanning a laser beam modulated according to an image signal onto a photosensitive drum as a recording medium.
Related Background Art
In recent years, recording apparatuses such as a laser beam printer (LBP) for recording an image by scanning a laser beam have been widely used.
A laser scanning device used in an image recording apparatus will be described below with reference to FIG. 11. A semiconductor laser light source 1, a collimator lens 2, an imaging optical system 3, a polygonal mirror 4 as a deflector, an f.theta. lens 5, and a photosensitive drum 6 as a recording medium are arranged along an optical path. A laser beam emitted from the semiconductor laser light source 1 and modulated according to an image signal is collimated into parallel light by the collimator lens 2, and is then deflected by the polygonal mirror 4. The laser beam is imaged and scanned on the photosensitive drum 6 by the f.theta. lens 5.
In general, since light output from a semiconductor laser light source radially diverges from a light emission point, when such light source is used in, e.g., an LBP, a laser beam output optical unit for collimating the output light into parallel light using a collimator lens is normally used. FIG. 12 is a longitudinal sectional view of such laser beam output optical unit. A semiconductor laser light source 1 is fixed to a light emission control circuit board 7 by an adhesive. The circuit board 7 is fixed to a laser base 8 by a screw 14. The laser base 8 is fixed to a lens barrel holder 9 by a screw 11 after its position in the direction perpendicular to output light is adjusted. A lens barrel 12 for holding a collimator lens is subjected to focus adjustment in the direction parallel to output light, and is then fixed to the lens barrel holder 9 by an adhesive. Conventionally, position adjustment of the output light is performed as follows. That is, as shown in FIG. 13, the output light is detected by a TV camera 15, and the position of the laser base is manually adjusted, so that a spot image 17 of the output light falls within an adjustment range frame 18 while observing the image on a monitor 16. Thereafter, the laser base is fixed by a screw.
Upon inspection of the laser scanning optical system including the laser beam output optical unit, beam evaluation is normally performed by enlarging the beam using an objective lens, and executing image processing of an area sensor signal so as to measure a beam diameter. At this time, in a conventional method, a beam is stopped, and a polygonal mirror is externally controlled until a beam enters a measurement area. In order to measure a beam at a plurality of positions (normally, three positions), a plurality of measurement systems must be arranged.
Before adjustment of the laser beam output optical unit, the light emission point of the laser is normally shifted by .+-.0.2 mm to .+-.0.3 mm from an imaginary light emission point calculated from the outer diameter of the lens barrel, and the initial position of output light on the TV camera is shifted by .+-.4 mm to .+-.6 mm depending on the magnification of the collimator lens 2 and the magnification of the objective lens of the TV camera 15. In contrast to this, the TV camera has a view field as small as 2.5 mm.sup.2 to improve measurement precision. Therefore, output light can hardly fall within the view field of the TV camera before adjustment, and adjustment must be started from an operation for causing the output light to fall within the view field of the TV camera. For this purpose, the position of the laser base is slowly moved in the direction perpendicular to the output light, so that laser light falls within the view field of the TV camera. Thereafter, fine adjustment is performed while observing the monitor 16. Such an operation requires a very long time period. When the laser base and the lens barrel holder are fixed by fastening a screw after adjustment, the position of the laser base is shifted upon final fastening of the screw, and re-adjustment must be performed, thus requiring another very long time period. The adjustment position may be initially shifted to compensate for an expected shift amount. However, such adjustment is performed by only a specialized person since a great deal of skills are required to determine the expected amount.